Cell

Some as small as one micrometer (µm). Most much smaller than one millimeter (mm).

Size is restricted by Surface/Volume (S/V) ratio

Surface is membrane, across which cell acquires
nutrients and expels wastes

Volume is living cytoplasm, which demands nutrients and produces wastes

As cell grows, volume increases faster than surface

Cells specialized in absorption modified to greatly increase surface area per unit volume

If the cell grows too large, the plasma membrane will not have sufficient surface area to support the rate of diffusion required for the increased volume. In other words, as a cell grows, it becomes less efficient.

Parts of Prokaryotic Cells

Glycocalyx - Layer of polysaccharides outside cell wall
May be slimy and easily removed, or
Well organized and resistant to removal (capsule)

Cell Wall

Plasma Membrane - Like in eukaryotes
Form internal pouches (mesosomes)

Semifluid solution, bounded by plasma membrane, contains inclusion bodies (stored granules of various substances)

Flagella – Provide motility

Fimbriae – small, bristle-like fibers that sprout
from the cell surface

Sex pili – rigid tubular structures used to pass
DNA from cell to cell

Parts of Eukaryotic Cells

Allows separation of cell parts
Separated out by size & density
Works like spin cycle of washer
The faster the machine spins, the smaller the parts that settled out

Command center of cell, usually near center
Separated from cytoplasm by nuclear
envelope
- Consists of double layer of membrane
- Nuclear pores permit exchange between nucleoplasm & cytoplasm

Contains chromatin in semifluid nucleoplasm
- Chromatin contains DNA of genes
- Condenses to form chromosomes

Dark nucleolus composed of rRNA
- Produces subunits of ribosomes

Serve in protein synthesis
Composed of rRNA
- Consists of a large subunit and a small subunit
- Subunits made in nucleolus

May be located:
- On the endoplasmic reticulum (thereby making it “rough”), or
- Free in the cytoplasm, either singly or in groups called polyribosomes

Similar to lysosomes: Membrane-bounded vesicles and enclosed enzymes
However, enzymes synthesized by free ribosomes in cytoplasm (instead of ER),
active in lipid metabolism, catalyze reactions that produce hydrogen peroxide H2O2, toxic, and broken down to water & O2 by catalase

Membranous sacs that are larger than
vesicles
- Store materials that occur in excess
- Others very specialized (contractile vacuole)
Plants cells typically have a central vacuole (Up to 90% volume of some cells)
Functions in: storage of water, nutrients, pigments, and waste products, development of turgor pressure, some functions performed by lysosomes in other eukaryotes

Maintains cell shape
Assists in movement of cell and organelles
Three types of macromolecular fibers
- Actin Filaments
- Intermediate Filaments
- Microtubules
Assemble and disassemble as needed

Extremely thin filaments like twisted pearl necklace. Dense web just under plasma membrane maintains cell shape. Support for microvilli in intestinal cells. Intracellular traffic control
*For moving stuff around within cell
*Cytoplasmic streaming
Function in pseudopods of amoeboid cells. Pinch mother cell in two after animal mitosis. Important component in muscle contraction (other is myosin)

Intermediate in size between actin filaments and microtubules
Rope-like assembly of fibrous polypeptides and varies in nature

Hollow cylinders made of two globular proteins called α and β tubulin
Spontaneous pairing of α and β tubulin molecules form structures called dimers. Dimers then arrange themselves into tubular spirals of 13 dimers around.

Microtubular Arrays

Short, hollow cylinders, composed of 27 microtubules, one pair per animal cell. May give rise to basal bodies of cilia and
flagella.

Hair-like projections from cell surface that aid
in cell movement (very different from prokaryote flagella). In eukaryotes, cilia are much shorter than
flagella

Two Classes:

Organelles that communicate with one another
Restrict enzymatic reactions to specific
compartments within cell
Consists of:
- Nuclear envelope
- Membranes of endoplasmic reticulum
- Golgi apparatus
- Vesicles
- Several types
- Transport materials between organelles of system

The Endoplasmic Reticulum

Studded with ribosomes on cytoplasmic side
Protein anabolism
- Synthesizes proteins
- Modifies proteins
- Adds sugar to protein
- Results in glycoproteins

No ribosomes
Synthesis of lipids

Consists of 3-20 flattened, curved saccules
Resembles stack of hollow pancakes
Modifies proteins and lipids
- Packages them in vesicles
- Receives vesicles from ER on cis face
- Prepares for “shipment” in vesicles from trans face
- Within cell
- Export from cell (secretion, exocytosis)

Membrane-bound vesicles (not in plants). Produced by the Golgi apparatus and has a low pH. Contain lytic enzymes:
- Digestion of large molecules
- Recycling of cellular resources
- Apoptosis (programmed cell death, like tadpole losing tail)
Some genetic diseases
- Caused by defect in lysosomal enzyme
- Lysosomal storage diseases (Tay-Sachs)

Mitochondria & chloroplasts. Basically independent & self-sufficient.

Captures light energy to drive cellular
machinery

Photosynthesis
- Synthesizes carbohydrates from CO2 & H2O
- Makes own food using CO2 as only carbon source
- Energy-poor compounds converted to energy rich compounds

Chloroplast Structure

Bounded by double membrane
Inner membrane infolded
- Forms disc-like thylakoids, which are stacked to form grana
- Suspended in semi-fluid stroma
Green due to chlorophyll
- Green photosynthetic pigment
- Found ONLY in inner membranes of chloroplast

Bounded by double membrane
- Cristae – Infoldings of inner membrane that
encloses matrix
- Matrix – Inner semifluid containing respiratory enzymes
Involved in cellular respiration
Produce most of ATP utilized by the cell

Two Domains

Live in extreme habitats

Shapes of Bacteria

Bacillus - rod-shaped bacteria

Coccus - spherical or oval bacteria

Spirillum - a thick, rigid spiral

Spirochete - similar to Spirillum but thin and flexible

Domain Eukarya

Kingdoms

Protists

Fungi

Plants

Animals

Cells Contain:

Membrane-bound nucleus
Specialized organelles
Plasma membrane

Hypothesized Origin

American biologist Lynn Margulis developed endosymbiotic theory, which states that eukaryotes may have been a product of one cell engulfing another, one living within another, and evolving over time until the separate cells were no longer recognizable as such.

Cell gains a nucleus by the plasma membrane invaginating and surrounding the DNA with a double membrane

Cell gains an endomembrane system by proliferation of membrane

Cell gains mitochondria

For plant cells, cell gains chloroplasts.

Technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye (objects that are not within the resolution range of the normal eye).

Terms

An instrument that magnifies an object. Most photographs of cells are taken with a microscope

Derived from "micro-"= small and "-scope"= to look at

Images taken by a Microscope

Explore the relationships between structures and properties for a very wide variety of materials.

The degree of fineness with which an image can be recorded or produced, often expressed as the number of pixels per unit of length (typically an inch).

Measure of how much larger a microscope (or set of lenses within a microscope) causes an object to appear.

Types of Microscopy

Light passed through specimen

Focused by glass lenses

Image formed on human retina

Max magnification about 1000X

Resolves objects separated by 0.2 µm, 500X better than human eye

Specimen sprayed with thin coat of metal (Electron beam scanned across surface of specimen

Metal emits secondary electrons

Emitted electrons focused by magnetic lenses

Image formed on fluorescent screen

Electrons passed through specimen

Focused by magnetic lenses

Image formed on fluorescent screen (Similar to TV screen, image is then photographed)

Max magnification 1000,000s X

Resolves objects separated by 0.00002 µm, 100,000X better than human eye

Antibodies developed against a specific protein

Fluorescent dye molecule attached to antibody
molecules

Specimen exposed to fluorescent antibodies
Ultra-violet light (black light) passed through specimen (Fluorescent dye glows in color where antigen is located, emitted light is focused by glass lenses onto human retina)

Allows mapping distribution of a specific protein in cell

Narrow laser beam scanned across transparent specimen

Beam is focused at a very thin plane

Allows microscopist to optically section a specimen (Sections made at different levels, allows assembly of 3D image on computer screen that can be rotated)

Great for specimens with low contrast, like living cells

Image is captured by TV camera instead of eye

Image is then “tweaked” by adjusting contrast

Darkest part of image is made black , lightest part of image is made white, all parts in between made shades of gray

Also allows various shades to be converted to different colors for more contrast

Great for transparent specimens with low
contrast, like living cells

Some organelles have higher density than others
(Speed of light is affected by density, light passes more slowly through high density than low density, light waves entering a specimen “in phase” exit some parts of the specimen out of phase)

Microscope shows only light that is slower or faster

Causes transparent organelles to “glow”

Parts of a Microscope

Eyepiece or Ocular Lens

Tube

Frame or Arm

Base

Illuminator

Mechanical Stage

Coarse Focus

Fine Focus

Objective Lenses

Revolving Nosepiece or Turret

Rack Stop

Condenser Lens

Diaphragm or Iris

A unifying concept in biology.
Originated from the work of biologists
Schleiden and Schwann in 1838-1839

States that:

All organisms are composed of cells

The cell is the basic unit of life

All cells arise from preexisting cells

The modern version includes:

Cells carry genetic material passed to daughter cells during cellular division

All cells are essentially the same in chemical composition

Energy flow (metabolism and biochemistry) occurs within cells

History

In the early 1600s, Zacharias Jansen invented the first microscope, though this is often disputed.

In 1665, Robert Hooke published Micrographia where he observed the cell structure of a thinly sliced cork. He coined the term "cell" because the structure reminded him of cells in monasteries

In 1675-1677, Anton Van Leeuwenhoek invented a microscope that could magnify a specimen 300x larger than its size. He observed dental scrapings and was the first to observe bacteria.

In 1830, Joseph Jackson Lister made improvements in the microscope by using several weak lenses at varying distances. This led to further progress in the development of the cell theory.

In 1831, Robert Brown discovered the nucleus. He also observed the erratic motion of pollen grain in water and coined the movement "Brownian Motion" .

In 1838-1839, Matthias Schleiden and Theodor Schwann co-developed the cell theory and concluded the first 2 core concepts of the cell theory.

In 1855, German physician Rudolf Virchow was studying cancer cells when he came to the conclusion that all cells come from pre-existing cells. This became the third core concept.